The above statements may be illustrated by way of an example, e.g. a digital voice and data transmission system. Assume a number of local voice terminals are to be attached to a digital transmission network. Each voice signal needs to be processed. It is first converted into digital form prior to being transmitted over the network. For that purpose the outgoing voice signal is submitted to more or less complex operations, designed to get the best voice coding quality, e.g. in terms of quantizing noise for a given bit rate. The processing workload required is fairly high, but it mainly consists in repetitive computing operations on the same data. For instance, the voice signal is processed by segments each 20 ms long. Each voice segment is sampled at, say, 8 KHz, and thus provides a block of 160 samples. Each sample is coded in PCM with 8 bits. Then each 20 ms, the whole block of PCM coded samples are reprocessed to lower the final number of bits required to code the same samples, while keeping the coding quality at the highest possible level.
A number of coders have been proposed to perform the above coding operations. One may refer for instance to European Pat. No. 0002998 (U.S. Pat. No. 4,216,354) to the same assignee for further details on these coders. But, with any of these coders, the rate of input/output operations is fairly limited (e.g. one operation per 20 ms) and requires little data transfers when compared with the processing workload required for compression and related signal processing operations.
A primary reason for doing the compression operations has to do with the high cost of transmission channels. Important savings can be made by compressing voice signal and concentrating (e.g. multiplexing) as many voices as possible on the same transmission channel. Consequently several voice coders can be attached to the same channel, through a Control Unit made to manage the interface operations between a set of Voice terminals (coders) and a common channel.
For the above cited coder example, for instance, the Control Unit would have to control the coders I/O operations, for transferring each 20 ms the bits derived from a voice segment processed by each of the signal processors attached to the same Control Unit.
These transfers could be made using different methods. Some of these methods would be fairly rigid, therefore not allow easy reconfiguration of the network in the field.
A system architecture is proposed here, which conveniently combines hard and soft devices enabling program parametering of the system to adjust to the specific system configuration required.
This architecture is not however limited to voice multiplexing operations.
It may be generically used in all machines where several processors execute Tasks which may be included in a fixed time frame.
The expression "signal processor" will thus be used in this application for this kind of processor, even if the executed task is not related to signal processing.